Die for coextruding a plurality of fluid layers

ABSTRACT

A die for coextruding a plurality of fluid layers generally includes a primary forming stem, one or more distribution plates, and a microlayer assembly. The microlayer assembly includes a microlayer forming stem and a plurality of microlayer distribution plates.

This application is a continuation of U.S. patent application Ser. No.12/284,510, filed Sep. 23, 2008, the disclosure of which is herebyincorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

The present invention relates to a coextrusion die and, moreparticularly, to a coextrusion die containing both a microlayer assemblyand one or more distribution plates to produce coextruded films havingboth microlayers and thicker, conventional film layers.

Coextrusion is a technique for producing a multilayer plastic(polymeric) film by bringing two or more molten polymers together in adie, in which the polymers are formed into a generally tubular or planarshape, juxtaposed in layered form, and then pushed out of an annular- orslot-shaped opening in the die. Once outside of the die, thestill-molten multilayer film is exposed to an environment having atemperature that is maintained below the melting point of the componentpolymeric layers of the film, which causes the layers to melt-bondtogether as they cool and solidify.

Multilayer films typically have a thickness in the range of 50-200 milsupon emergence from the die, but the films are generally stretched priorto final solidification in order to expand their surface area and reducetheir final thickness to a range of about 0.5 to about 50 mils.Conventional multilayer films generally have 3-10 layers; prior tostretching and thinning, i.e., while still in the die, each such layergenerally ranges from about 20-100 mils in thickness.

Microlayer extrusion is a technique for increasing the total number oflayers in a multilayer film for a given film thickness, by reducing thethickness of the component layers of the film. Thus, while conventionalfilm layers generally range from 20-100 mils inside the die (i.e., priorto stretching and thinning), microlayers generally have an ‘in-die’thickness ranging from about 1-20 mils. In this manner, microlayeredfilms may have far more than 10 layers, e.g., 20, 30, 40, 50, or morelayers. Such microlayered films have been found to provide certainbeneficial properties relative to conventional films composed of thickerlayers that are fewer in number, e.g., improved mechanical propertiessuch as superior flex cracking and puncture resistance.

For many applications, it is desirable to combine thicker, conventionallayers with microlayers. Such thicker layers are often superior tomicrolayers for functions such as heat-sealing and abuse-resistance.

Unfortunately, it has proven to be difficult to combine the flow of thinlayers, such as microlayers, with relatively thick layers in such a waythat the physical integrity and independent properties of the thinlayers are maintained. This is primarily the result of interfacial flowinstabilities, which are encountered when microlayers are mergedtogether with thicker layers in a die. Such interfacial flowinstabilities are caused by the more powerful sheer forces of thethicker layers flowing against the microlayers, which result from thehigher mass flow rate of the thicker layers relative to the microlayers.The resultant loss of the integrity and independent characteristics ofthe microlayers diminishes or even eradicates the beneficial propertiesthereof.

Accordingly, there is a need in the art for an improved die that permitsmicrolayers to be combined with conventional, thicker layers in such away that the integrity and independent properties of the microlayers aremaintained.

SUMMARY OF THE INVENTION

That need is met by the present invention, which, in one aspect,provides a die for coextruding a plurality of fluid layers, comprising;

a. a primary forming stem;

b. one or more distribution plates, each of the plates having a fluidinlet and a fluid outlet, the fluid outlet from each of the plates beingin fluid communication with the primary forming stem and structured todeposit a layer of fluid onto the primary forming stem; and

c. a microlayer assembly, comprising

-   -   (1) a microlayer forming stem, and    -   (2) a plurality of microlayer distribution plates, each of the        microlayer plates having a fluid inlet and a fluid outlet, the        fluid outlet from each of the microlayer plates being in fluid        communication with the microlayer forming stem and structured to        deposit a microlayer of fluid onto the microlayer forming stem,        the microlayer plates being arranged to provide a predetermined        order in which the microlayers are deposited onto the microlayer        forming stem to form a substantially unified, microlayered fluid        mass on the microlayer forming stem,

wherein, the microlayer forming stem is in fluid communication with theprimary forming stem such that the microlayered fluid mass flows fromthe microlayer forming stem and onto the primary forming stem.

Another aspect of the invention is directed to a system for coextrudinga plurality of fluid layers, comprising a die as described above, andone or more extruders in fluid communication with the die to supply oneor more fluids to the die.

A further aspect of the invention pertains to a method of coextruding aplurality of fluid layers, comprising:

a. directing a fluid through a distribution plate and onto a primaryforming stem, the distribution plate having a fluid inlet and a fluidoutlet, the fluid outlet from the plate being in fluid communicationwith the primary forming stem and structured such that the fluid isdeposited onto the primary forming stem as a layer;

b. forming a substantially unified, microlayered fluid mass on amicrolayer forming stem by directing at least one additional fluidthrough a microlayer assembly, the microlayer assembly comprising aplurality of microlayer distribution plates, each of the microlayerplates having a fluid inlet and a fluid outlet, the fluid outlet fromeach of the microlayer plates being in fluid communication with themicrolayer forming stem and structured to deposit a microlayer of fluidonto the microlayer forming stem, the microlayer plates being arrangedto provide a predetermined order in which the microlayers are depositedonto the microlayer forming stem; and

c. directing the microlayered fluid mass from the microlayer formingstem and onto the primary forming stem to merge the microlayered fluidmass with the fluid layer from the distribution plate.

These and other aspects and features of the invention may be betterunderstood with reference to the following description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of a system 10 in accordance with the presentinvention for coextruding a plurality of fluid layers, including a die12;

FIG. 2 is a cross-sectional view of the die 12 shown in FIG. 1;

FIG. 3 is a plan view one of the microlayer plates 48 in die 12;

FIG. 4 is a cross-sectional view of the microlayer plate 48 shown inFIG. 3; and

FIG. 5 is a magnified, cross-sectional view of die 12, showing thecombined flows from the microlayer plates 48 and distribution plates 32.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a system 10 in accordance with thepresent invention for coextruding a plurality of fluid layers. System 10generally includes a die 12 and one or more extruders 14 a and 14 b influid communication with the die 12 to supply one or more fluids to thedie.

In a typical application, the fluid layers coextruded by die 12 maycomprise one or more molten thermoplastic polymers. Examples of suchpolymers include polyolefins, polyesters (e.g., PET), polystyrenes,polyamide homopolymers and copolymers (e.g. PA6, PA12, PA6/12, etc.),polycarbonates, etc. Within the family of polyolefins, variouspolyethylene homopolymers and copolymers may be used, as well aspolypropylene homopolymers and copolymers (e.g., propylene/ethylenecopolymer). Polyethylene homopolymers may include low densitypolyethylene (LDPE) and high density polyethylene (HDPE). Suitablepolyethylene copolymers may include a wide variety of polymers, such as,e.g., ionomers, ethylene/vinyl acetate (EVA), ethylene/vinyl alcohol(EVOH), and ethylene/alpha-olefins, including heterogeneous(Zeigler-Natta catalyzed) and homogeneous (metallocene, single-citecatalyzed) ethylene/alpha-olefin copolymers. Ethylene/alpha-olefincopolymers are copolymers of ethylene with one or more comonomersselected from C₃ to C₂₀ alpha-olefins, such as 1-butene, 1-pentene,1-hexene, 1-octene, methyl pentene and the like, including linear lowdensity polyethylene (LLDPE), linear medium density polyethylene(LMDPE), very low density polyethylene (VLDPE), and ultra-low densitypolyethylene (ULDPE).

As is conventional, the polymeric materials may be supplied to theextruders 14 a, b in the solid-state, e.g., in the form of pellets orflakes, via respective hoppers 16 a, b. Extruders 14 a, b are maintainedat a temperature sufficient to convert the solid-state polymer to amolten state, and internal screws within the extruders (not shown) movethe molten polymer into and through die 12 via respective pipes 18 a, b.As will be explained in further detail below, within die 12, the moltenpolymer is converted into thin film layers, and each of the layers aresuperimposed, combined together, and expelled from the die at dischargeend 20, i.e., “coextruded,” to form a tubular, multilayer film 22. Uponemergence from the die 12 at discharge end 20, the tubular, multilayerfilm 22 is exposed to ambient air or a similar environment having atemperature sufficiently low to cause the molten polymer from which thefilm is formed to transition from a liquid state to a solid state.Additional cooling/quenching of the film may be achieved by providing aliquid quench bath (not shown), and then directing the film through suchbath.

The solidified tubular film 22 is then collapsed by a convergence device24, e.g., a V-shaped guide as shown, which may contain an array ofrollers to facilitate the passage of film 22 therethrough. A pair ofcounter-rotating drive rollers 25 a, b may be employed as shown to pullthe film 22 through the convergence device 24. The resultant collapsedtubular film 22 may then be wound into a roll 26 by a film windingdevice 28 as shown. The film 22 on roll 26 may subsequently be unwoundfor use, e.g., for packaging, or for further processing, e.g.,stretch-orientation, irradiation, or other conventional film-processingtechniques, which are used to impart desired properties as necessary forthe intended end-use applications for the film.

Referring now to FIG. 2, die 12 will be described in further detail. Asnoted above, die 12 is adapted to coextrude a plurality of fluid layers,and generally includes a primary forming stem 30, one or moredistribution plates 32, and a microlayer assembly 34. In the presentlyillustrated die, five distribution plates 32 are included, asindividually indicated by the reference numerals 32 a-e. A greater orlesser number of distribution plates 32 may be included as desired. Thenumber of distribution plates in die 12 may range, e.g., from one totwenty, or even more then twenty if desired.

Each of the distribution plates 32 has a fluid inlet 36 and a fluidoutlet 38 (the fluid inlet is not shown in plate 32 b). The fluid outlet38 from each of the distribution plates 32 is in fluid communicationwith the primary forming stem 30, and also is structured to deposit alayer of fluid onto the primary forming stem. The distribution plates 32may be constructed as described in U.S. Pat. No. 5,076,776, the entiredisclosure of which is hereby incorporated herein by reference thereto.As described in the '776 patent, the distribution plates 32 may have oneor more spiral-shaped fluid-flow channels 40 to direct fluid from thefluid inlet 36 and onto the primary forming stem 30 via the fluid outlet38. As the fluid proceeds along the channel 40, the channel becomesprogressively shallower such that the fluid is forced to assume aprogressively thinner profile. The fluid outlet 38 generally provides arelatively narrow fluid-flow passage such that the fluid flowing out ofthe plate has a final desired thickness corresponding to the thicknessof the fluid outlet 38. Other channel configurations may also beemployed, e.g., a toroid-shaped channel; an asymmetrical toroid, e.g.,as disclosed in U.S. Pat. No. 4,832,589; a heart-shaped channel; ahelical-shaped channel, e.g., on a conical-shaped plate as disclosed inU.S. Pat. No. 6,409,953, etc. The channel(s) may have a semi-circular orsemi-oval cross-section as shown, or may have a fuller shape, such as anoval or circular cross-sectional shape.

In some embodiments, distribution plates 32 may have a generally annularshape such that the fluid outlet 38 forms a generally ring-likestructure, which forces fluid flowing through the plate to assume aring-like form. Such ring-like structure of fluid outlet 38, incombination with its proximity to the primary forming stem 30, causesthe fluid flowing through the plate 32 to assume a cylindrical shape asthe fluid is deposited onto the stem 30. Each flow of fluid from each ofthe distribution plates 32 thus forms a distinct cylindrical layer onthe primary forming stem 30.

The fluid outlets 38 of the distribution plates 32 are spaced from theprimary forming stem 30 to form an annular passage 42. The extent ofsuch spacing is sufficient to accommodate the volume of the concentricfluid layers flowing along the forming stem 30.

The order in which the distribution plates 32 are arranged in die 12determines the order in which the fluid layers are deposited onto theprimary forming stem 30. For example, if all five distribution plates 32a-e are supplied with fluid, fluid from plate 32 a will be the first tobe deposited onto primary forming stem 30 such that such fluid will bein direct contact with the stem 30. The next layer to be deposited ontothe forming stem would be from distribution plate 32 b. This layer willbe deposited onto the fluid layer from plate 32 a. Next, fluid fromplate 32 c will be deposited on top of the fluid from plate 32 b. Ifmicrolayer assembly 34 were not present in the die, the next layer to bedeposited would be from distribution plate 32 d, which would be layeredon top of the fluid layer from plate 32 c. Finally, the last and,therefore, outermost layer to be deposited would be from plate 32 e. Inthis example (again, ignoring the microlayer assembly 34), the resultanttubular film 22 that would emerge from the die would have five distinctlayers, which would be arranged as five concentric cylinders bondedtogether.

Accordingly, it may be appreciated that the fluid layers from thedistribution plates 32 are deposited onto the primary forming stem 30either directly (first layer to be deposited, e.g., from distributionplate 32 a) or indirectly (second and subsequent layers, e.g., fromplates 32 b-e).

As noted above, the tubular, multilayer film 22 emerges from die 12 atdischarge end 20. The discharge end 20 may thus include an annulardischarge opening 44 to allow the passage of the tubular film 22 out ofthe die. Such annular discharge opening is commonly referred to as a“die lip.” As illustrated, the diameter of the annular discharge opening44 may be greater than that of the annular passage 42, e.g., to increasethe diameter of the tubular film 22 to a desired extent. This has theeffect of decreasing the thickness of each of the concentric layers thatmake up the tubular film 22, i.e., relative to the thickness of suchlayers during their residence time within the annular passage 42.Alternatively, the diameter of the annular discharge opening 44 may besmaller than that of the annular passage 42.

Microlayer assembly 34 generally comprises a microlayer forming stem 46and a plurality of microlayer distribution plates 48. In the presentlyillustrated embodiment, fifteen microlayer distribution plates 48 a-oare shown. A greater or lesser number of microlayer distribution plates48 may be included as desired. The number of microlayer distributionplates 48 in microlayer assembly 34 may range, e.g., from one to fifty,or even more then fifty if desired. In many embodiments of the presentinvention, the number of microlayer distribution plates 48 in microlayerassembly 34 will be at least about 5, e.g., 10, 15, 20, 25, 30, 35, 40,45, 50, etc., or any number of plates in between the foregoing numbers.

Each of the microlayer plates 48 has a fluid inlet 50 and a fluid outlet52. The fluid outlet 52 from each of the microlayer plates 48 is influid communication with microlayer forming stem 46, and is structuredto deposit a microlayer of fluid onto the microlayer forming stem.Similar to the distribution plates 32, the microlayer plates 48 may alsobe constructed as described in the above-incorporated U.S. Pat. No.5,076,776.

For example, as shown in FIG. 3, the microlayer plates 48 may have aspiral-shaped fluid-flow channel 54, which is supplied with fluid viafluid inlet 50. Alternatively, two more fluid-flow channels may beemployed in plate 48, which may be fed from separate fluid inlets or asingle fluid inlet. Other channel configurations may also be employed,e.g., a toroid-shaped channel; an asymmetrical toroid, e.g., asdisclosed in U.S. Pat. No. 4,832,589; a heart-shaped channel; ahelical-shaped channel, e.g., on a conical-shaped plate as disclosed inU.S. Pat. No. 6,409,953; etc. The channel(s) may have a semi-circular orsemi-oval cross-section as shown, or may have a fuller shape, such as anoval or circular cross-sectional shape.

Regardless of the particular configuration or pattern that is selectedfor the flow channel(s) 54, its function is to connect the fluidinlet(s) 50 with the fluid outlet 52 in such a manner that the flow offluid through the microlayer assembly 34 is converted from a generallystream-like, axial flow to a generally film-like, convergent radial flowtowards the microlayer forming stem 46. Microlayer plate 48 as shown inFIG. 3 may accomplish this in two ways. First, the channel 54 spiralsinwards towards the center of the plate, and thus directs fluid from thefluid inlet 50, located near the periphery of the plate, towards thefluid outlet 52, which is located near the center of the plate.Secondly, the channel 54 may be fashioned with a progressively shallowerdepth as the channel approaches the fluid outlet 52. This has the effectof causing some of the fluid flowing through the channel 54 to overflowthe channel and proceed radially-inward toward the fluid outlet 52 in arelatively flat, film-like flow. Such radial-inward flow may occur inoverflow regions 53, which may be located between the spaced-apartspiral sections of channel 54. As shown in FIG. 4, the overflow regions53 may be formed as recessed sections in plate 48, i.e., recessedrelative to the thicker, non-recessed region 55 at the periphery of theplate. As shown in FIG. 3, overflow regions 53 may begin at step-down 57and, e.g., spiral inwards towards fluid outlet 52 between the spirals ofchannel 54. The non-recessed, peripheral region 55 abuts against theplate or other structure above the plate, e.g., as shown in FIGS. 2 and5, and thus prevents fluid from flowing outside the periphery of theplate. In this manner, the non-recessed, peripheral region 55 forcesfluid entering the plate to flow radially inward toward fluid outlet 52.Step-down 57 thus represents a line or zone of demarcation between the‘no-flow’ peripheral region 55 and the ‘flow’ regions 53 and 54. Thefluid that remains in the channel 54 and reaches the end 56 of thechannel flows directly into the fluid outlet 52.

The fluid outlet 52 generally provides a relatively narrow fluid-flowpassage and generally determines the thickness of the microlayer flowingout of the microlayer plate 48. The thickness of the fluid outlet 52,and therefore the thickness of the microlayer flowing therethrough, maybe determined, e.g., by the spacing between the plate surface at outlet52 and the bottom of the plate or other structure (e.g., manifold 76 or78) immediately above the plate surface at outlet 52.

With continuing reference to FIGS. 2-3, each of the microlayerdistribution plates 48 may have an orifice 58 extending through theplate. The orifice 58 may be located substantially in the center of eachmicrolayer plate 48, with the fluid outlet 52 of each plate positionedadjacent to such orifice 58. In this manner, the microlayer forming stem46 may extend through the orifice 58 of each of the microlayerdistribution plates 48. With such a configuration, the microlayerdistribution plates 48 may have a generally annular shape such that thefluid outlet 52 forms a generally ring-like structure, which forcesfluid flowing through the plate to exit the plate in aradially-convergent, ring-like flow pattern. Such ring-like structure offluid outlet 52, in combination with its proximity to the microlayerforming stem 46, causes the fluid exiting the microlayer plates 48 toassume a cylindrical shape as the fluid is deposited onto the microlayerstem 46. Each flow of fluid from each of the microlayer distributionplates 48 thus deposits a distinct cylindrical microlayer on themicrolayer forming stem 46.

The microlayer plates 48 may be arranged to provide a predeterminedorder in which the microlayers are deposited onto the microlayer formingstem 46. For example, if all fifteen microlayer distribution plates 48a-o are supplied with fluid, a microlayer of fluid from plate 48 a willbe the first to be deposited onto microlayer forming stem 46 such thatsuch microlayer will be in direct contact with the stem 46. The nextmicrolayer to be deposited onto the forming stem would be frommicrolayer plate 48 b. This microlayer will be deposited onto themicrolayer from plate 48 a. Next, fluid from microlayer plate 48 c willbe deposited on top of the microlayer from plate 48 b, etc. The lastand, therefore, outermost microlayer to be deposited is from plate 48 o.In this manner, the microlayers are deposited onto the microlayerforming stem 46 in the form of a substantially unified, microlayeredfluid mass 60 (see FIG. 5). In the present example, such microlayeredfluid mass 60 would comprise up to fifteen distinct microlayers (at thedownstream end of stem 46), arranged as fifteen concentric cylindricalmicrolayers bonded and flowing together in a predetermined order (basedon the ordering of the microlayer plates 48 a-o) on microlayer formingstem 46.

It may thus be appreciated that the fluid layers from the microlayerdistribution plates 48 are deposited onto the microlayer forming stem 46either directly (the first layer to be deposited, e.g., from microlayerplate 48 a) or indirectly (the second and subsequent layers, e.g., frommicrolayer plates 48 b-o). The orifices 58 in each of the microlayerplates 48 are preferably large enough in diameter to space the fluidoutlets 52 of the microlayer plates 48 sufficiently from the microlayerforming stem 46 to form an annular passage 62 for the microlayers (FIG.2). The extent of such spacing is preferably sufficient to accommodatethe volume of the concentric microlayers flowing along the microlayerstem 46.

In accordance with the present invention, microlayer forming stem 46 isin fluid communication with primary forming stem 30 such that themicrolayered fluid mass 60 flows from the microlayer forming stem 46 andonto the primary forming stem 30. This may be seen in FIG. 5, whereinmicrolayered fluid mass 60 from microlayer assembly 34 is shown flowingfrom microlayer forming stem 46 and onto primary forming stem 30. Fluidcommunication between the microlayer stem 46 and primary stem 30 may beachieved by including in die 12 an annular transfer gap 64 between theannular passage 62 for the microlayer stem 46 and the annular passage 42for the primary stem 30 (see also FIG. 2). Such transfer gap 64 allowsthe microlayered fluid mass 60 to flow out of the annular passage 62 andinto the annular passage 42 for the primary forming stem 30. In thismanner, the microlayers from microlayer plates 48 are introduced as aunified mass into the generally larger volumetric flow of the thickerfluid layers from the distribution plates 32.

The inventors have discovered that combining the flows of themicrolayers with the thicker fluid layers in this fashion minimizes thedeleterious effects of interfacial flow instabilities, which generallymake it difficult to combine the flow of thin layers with relativelythick layers in such a way that the physical integrity and independentproperties of the thin layers are maintained. The microlayer formingstem 46 allows the microlayers from the microlayer plates 48 to assembleinto the microlayered fluid mass 60 in relative calm, i.e., withoutbeing subjected to the more powerful sheer forces of the thicker layersflowing from the distribution plates 32. As the microlayers assembleinto the unified fluid mass 60 on stem 46, the interfacial flowinstabilities created by the merger of each layer onto the fluid mass 60are minimized because all the microlayers have a similar degree ofthickness, i.e., relative to the larger degree of thickness of the fluidlayers from distribution plates 32. When fully assembled, themicrolayered fluid mass 60 enters the flow of the thicker layers fromdistribution plates 32 on primary stem 30 with a mass flow rate thatmore closely approximates that of such thicker layers, therebyincreasing the ability of the microlayers in fluid mass 60 to retaintheir physical integrity and independent physical properties.

As shown in FIG. 2, primary forming stem 30 and microlayer forming stem46 may be substantially coaxially aligned with one another in die 12,e.g., with the microlayer forming stem 46 being external to the primaryforming stem 30. This construction provides a relatively compactconfiguration for die 12, which can be highly advantageous in view ofthe stringent space constraints that exist in the operating environmentof many commercial coextrusion systems.

For example, the coaxial alignment of the primary forming stem 30 withthe microlayer forming stem 46 allows the distribution plates 32 and themicrolayer assembly 34 to be axially positioned along the primaryforming stem, as shown in FIG. 2. This reduces the width of die 12, andalso allows the fluids from both the distribution plates 32 and themicrolayer assembly 34 to flow in an axial direction, e.g., in parallelpaths along primary forming stem 30 and microlayer forming stem 46, thentogether along the primary stem 30 downstream of transfer gap 64, atwhich the microlayered fluid mass 60 flows from the microlayer stem 46and onto the primary stem 30 to merge with the fluid layers from thedistribution plates 32.

Such construction also allows die 12 to be set up in a variety ofdifferent configurations to produce a coextruded film having a desiredcombination of thick layers and microlayers. For example, one or moredistribution plates 32 may be located upstream of the microlayerassembly 34. In this embodiment, fluid layers from such upstreamdistribution plates are deposited onto primary forming stem 30 prior tothe deposition of the microlayered fluid mass 60 onto the primary stem30. With reference to FIG. 2, it may be seen that distribution plates 32a-c are located upstream of microlayer assembly 34 in die 12. Fluidlayers 65 from such upstream distribution plates 32 a-c are thusinterposed between the microlayered fluid mass 60 and the primaryforming stem 30 (see FIG. 5).

Alternatively, the microlayer assembly 34 may be located upstream of thedistribution plates 32, i.e., the distribution plates may be locateddownstream of the microlayer assembly 34 in this alternative embodiment.Thus, the microlayers from the microlayer assembly 34, i.e., themicrolayered fluid mass 60, will be deposited onto primary forming stem30 prior to the deposition thereon of the fluid layers from thedownstream distribution plates 32. With reference to FIG. 2, it may beseen that microlayer assembly 34 is located upstream of distributionplates 32 d-e in die 12. As shown in FIG. 5, the microlayered fluid mass60 is thus interposed between the fluid layer(s) 70 from suchdistribution plates 32 d-e and the primary forming stem 30.

As illustrated in FIG. 2, the microlayer assembly 34 may also bepositioned between one or more upstream distribution plates, e.g.,plates 32 a-c, and one or more downstream distribution plates, e.g.,plates 32 d-e. In this embodiment, fluid(s) from upstream plates 32 a-care deposited first onto primary stem 30, followed by the microlayeredfluid mass 60 from the microlayer assembly 34, and then further followedby fluid(s) from downstream plates 32 d-e. In the resultant multilayeredfilm, the microlayers from microlayer assembly 34 are sandwiched betweenthicker layers from both the upstream plates 32 a-c and the downstreamplates 32 d-e.

As a further variation, die 12 may include one or more additionalmicrolayer assemblies, which may be the same as microlayer assembly 34or may have a different configuration, e.g., a different number ofmicrolayer plates. In this embodiment, any such additional microlayerassemblies may be coaxially aligned with the primary forming stem 30,and may be positioned upstream and/or downstream of the microlayerassembly 34 shown in FIG. 2. Such additional microlayer assemblies maybe used in place of or in addition to the distribution plates 32. Thus,additional microlayer assemblies may be positioned adjacent to themicrolayer assembly 34, or may be spaced from such assembly 34 by one ormore distribution plates 32. If two or more microlayer assemblies areincluded in die 12, such assemblies may also be sandwiched betweenupstream and downstream distribution plates, e.g., between the upstreamplates 32 a-c and downstream plates 32 d-e shown in FIG. 2.

In many embodiments of the invention, most or all of the microlayerplates 48 have a thickness that is less than that of the distributionplates 32. Thus, for example, the distribution plates 32 may have athickness T₁ (see FIG. 5) ranging from about 0.5 to about 2 inches,e.g., greater than 0.5 inch, such as 0.501 or more, 0.502 or more, 0.503or more, etc., or less than 2, e.g., 1.999 or less, 1.998 or less, etc.,such as from about 0.501 to 1.999 inches, 0.502 to 1.998 inches, etc.The microlayer distribution plates 48 may have a thickness T₂ rangingfrom about 0.1 to about 0.5 inch, e.g., greater than 0.1, such as 0.101or more, 0.102 or more, etc., or less than 0.5, e.g., 0.499 or less,0.498 or less, etc., such as from about 0.101 to 0.499 inch, 0.102 to0.498 inch, etc. Such thickness ranges are not intended to be limitingin any way, but only to illustrate typical examples. All distributionplates 32 will not necessarily have the same thickness, nor will all ofthe microlayer plates 48. For example, microlayer plate 48 o, the mostdownstream of the microlayer plates in the assembly 34, may be thickerthan the other microlayer plates to accommodate a sloped contact surface66, which may be employed to facilitate the transfer of microlayeredfluid mass 60 through the annular gap 64 and onto the primary formingstem 30.

As also shown in FIG. 5, each of the microlayers flowing out of theplates 48 has a thickness “M” corresponding to the thickness of thefluid outlet 52 from which each microlayer emerges. The microlayersflowing from the microlayer plates 48 are schematically represented inFIG. 5 by the phantom arrows 68.

Similarly, each of the relatively thick fluid layers flowing out of theplates 32 has a thickness “D” corresponding to the thickness of thefluid outlet 38 from which each such layer emerges (see FIG. 5). Therelatively thick fluid layers flowing from the distribution plates 32are schematically represented in FIG. 5 by the phantom arrows 70.

Generally, the thickness M of the microlayers will be less than thethickness D of the fluid layers from the distribution plates 32. Thethinner that such microlayers are relative to the fluid layers from thedistribution plates 32, the more of such microlayers that can beincluded in a multilayer film, for a given overall film thickness.Microlayer thickness M from each microlayer plate 48 will generallyrange from about 1-20 mils (1 mil=0.001 inch), e.g., greater than 1 mil,greater than 2 mils, greater than 3 mils, etc., less than 20 mils, lessthan 19 mils, less than 18 mils, etc., such as between 2 to 19 mils, 3to 18 mils, 4 to 17 mils, etc. Thickness D from each distribution plate32 will generally range from about 20-100 mils, e.g., greater than 20mils, greater than 21 mils, greater than 22 mils, etc., less than 100mils, less than 90 mils, less than 80 mils, less than 70 mils, less than60 mils, etc., such as between 20 to 50 mils, 21 to 49 mils, 22 to 48mils, 23 to 47 mils, etc. The foregoing thicknesses are not intended tobe limiting of the scope of the present invention in any way, and areprovided solely for illustration purposes.

The ratio of M:D may range from about 1:1 to about 1:8, e.g., greaterthan 1:1, greater than 1:1.1, greater than 1:1.2, greater than 1:2,greater than 1:3, etc., less than 1:8, less than 1:7.9, less than 1:7.8,less than 1:7, less than 1:6, etc., such as between 1:1.1-1:7.9;1:1.2-1:7.8, 1:2-1:7, 1:3-1:6, 1:4-1:5, etc.

Thickness M may be the same or different among the microlayers 68flowing from microlayer plates 48 to achieve a desired distribution oflayer thicknesses in the microlayer section of the resultant film.Similarly, thickness D may be the same or different among the thickerlayers 70 flowing from the distribution plates 32 to achieve a desireddistribution of layer thicknesses in the ‘thick-layer section(s)’ of theresultant film. The layer thicknesses M and D will typically change asthe fluid flows downstream through the die, e.g., if the melt tube isexpanded at annular discharge opening 44 as shown in FIG. 2, and/or uponfurther downstream processing of the tubular film, e.g., by stretching,orienting, or otherwise expanding the tube to achieve a final desiredfilm thickness and/or to impart desired properties into the film. Suchdownstream processing techniques are well known in the art. The flowrate of fluids through the plates will also have an effect on the finaldownstream thicknesses of the corresponding film layers.

With reference back to FIGS. 1-2, it may be appreciated that a method ofcoextruding a plurality of fluid layers in accordance with the presentinvention comprises the steps of:

a. directing one or more fluids through one or more distribution plates32 and onto primary forming stem 30 in die 12;

b. forming a substantially unified, microlayered fluid mass 60 onmicrolayer forming stem 46 by directing at least one additional fluidthrough microlayer assembly 34; and

c. directing the microlayered fluid mass 60 from the microlayer formingstem 46 and onto the primary forming stem 30 to merge the microlayeredfluid mass 60 with the fluid layer(s) from the distribution plate(s) 32.

As described above, the distribution plates 32 and microlayer plates 48preferably have an annular configuration, such that primary forming stem30 and microlayer stem 46 pass through the center of the plates toreceive fluid that is directed into the plates. The fluid may besupplied from extruders, such as extruders 14 a, b. The fluid may bedirected into the die 12 via vertical supply passages 72, which receivefluid from feed pipes 18, and direct such fluid into the die plates 32and 48. For this purpose, the plates may have one or more through-holes74, e.g., near the periphery of the plate as shown in FIG. 3, which maybe aligned to provide the vertical passages 72 through which fluid maybe directed to one or more downstream plates.

Although three through-holes 74 are shown in FIG. 3, a greater or lessernumber may be employed as necessary, e.g., depending upon the number ofextruders that are employed. In general, one supply passage 72 may beused for each extruder 14 that supplies fluid to die 12. The extruders14 may be arrayed around the circumference of the die, e.g., like thespokes of a wheel feeding into a hub, wherein the die is located at thehub position.

With reference to FIG. 1, die 12 may include a primary manifold 76 toreceive the flow of fluid from the extruders 14 via feed pipes 18, andthen direct such fluid into a designated vertical supply passage 72, inorder to deliver the fluid to the intended distribution plate(s) 32and/or microlayer plate(s) 48. The microlayer assembly 34 may optionallyinclude a microlayer manifold 78 to receive fluid directly from one ormore additional extruders 80 via feed pipe 82 (shown in phantom in FIG.1).

In the example illustrated in FIGS. 1-2, extruder 14 b delivers a fluid,e.g., a first molten polymer, directly to the fluid inlet 36 ofdistribution plate 32 a via pipe 18 b and primary manifold 76. In thepresently illustrated embodiment, distribution plate 32 a receives allof the output from extruder 14 b, i.e., such that the remaining platesand microlayer plates in the die 12 are supplied, if at all, from otherextruders. Alternatively, the fluid inlet 36 of distribution plate 32 amay be configured to contain an outlet port to allow a portion of thesupplied fluid to pass through to one or more additional plates, e.g.,distribution plates 32 and/or microlayer plates 48, positioneddownstream of distribution plate 32 a.

For example, as shown in FIGS. 3-4 with respect to the illustratedmicrolayer plate 48, an outlet port 84 may be formed in the base of thefluid inlet 50 of the plate. Such outlet port 84 allows the flow offluid delivered to plate 48 to be split: some of the fluid flows intochannel 54 while the remainder passes through the plate for delivery toone or more additional downstream plates 48 and/or 32. A similar outletport can be included in the base of the fluid inlet 36 of a distributionplate 32. Delivery of fluid passing through the outlet port 84 (orthrough a similar outlet port in a distribution plate 32) may beeffected via a through-hole 74 in an adjacent plate (see FIG. 5), or viaother means, e.g., a lateral-flow supply plate, to direct the fluid inan axial, radial, and/or tangential direction through die 12 asnecessary to reach its intended destination.

Distribution plates 32 b-c are being supplied with fluid via extruder(s)and supply pipe(s) and/or through-holes that are not shown in FIG. 2.The fluid flow along primary forming stem 30 from distribution plates 32a-c is shown in FIG. 5, as indicated by reference numeral 65.

As shown in FIGS. 1-2, microlayer assembly 34 is being supplied withfluid by extruders 14 a and 80. Specifically, microlayer plates 48 a, c,e, g, i, k, m, and o are supplied by extruder 14 a via supply pipe 18 aand vertical pipe and/or passage 72. Microlayer plates 48 b, d, f, h, j,l, and n are supplied with fluid by extruder 80 via feed pipe 82 and avertical supply passage 86. In the illustrated embodiment, verticalpassage 86 originates in microlayer manifold 78 and delivers fluid onlywithin the microlayer assembly 34. In contrast, vertical passage 72originates in manifold 76, extends through distribution plates 32 a-c(via aligned through-holes 74 in such plates), then further extendsthrough manifold 78 via manifold passage 79 before finally arriving atmicrolayer plate 48 a.

Fluid from extruder 14 a and vertical passage 72 enters microlayer plate48 a at fluid inlet 50. Some of the fluid passes from inlet 50 and intochannel 54 (for eventual deposition on microlayer stem 46 as the firstmicrolayer to be deposited on stem 46), while the remainder of the fluidmay pass through plate 48 a via outlet port 84. Microlayer plate 48 bmay be oriented, i.e., rotated, such that a through-hole 74 ispositioned beneath the outlet port 84 of microlayer plate 48 a so thatthe fluid flowing out of the outlet port 84 flows through the microlayerplate 48 b, and not into the channel 54 thereof. Microlayer plate 48 cmay be positioned such that the fluid inlet 50 thereof is in the samelocation as that of microlayer plate 48 a so that fluid flowing out ofthrough-hole 74 of microlayer plate 48 b flows into the inlet 50 ofplate 48 c. Some of this fluid flows into the channel 54 of plate 48 cwhile some of the fluid passes through the plate via outlet port 84,passes through a through-hole 74 in the next plate 48 d, and is receivedby fluid inlet 50 of the next microlayer plate 48 e, where some of thefluid flows into channel 54 and some passes out of the plate via outletport 84. Fluid from extruder 14 a continues to be distributed toremaining plates 48 g, i, k, and m in this manner, except for microlayerplate 48 o, which has no outlet port 84 so that fluid does not passthrough plate 48 o, except via channel 54 and fluid outlet 52.

In a similar manner, fluid from extruder 80 and vertical passage 86passes through microlayer plate 48 a via a through-hole 74 and thenenters microlayer plate 48 b at fluid inlet 50 thereof. Some of thisfluid flows through the channel 54 and exits the plate at outlet 52, tobecome the second microlayer to be deposited onto microlayer stem 46 (ontop of the microlayer from plate 48 a), while the remainder of the fluidpasses through the plate via an outlet port 84. Such fluid may passthrough microlayer plate 48 c via a through-hole 74, and be delivered toplate 48 d via appropriate alignment of its inlet 50 with thethrough-hole 74 of plate 48 c, through which the fluid from extruder 80passes. This fluid-distribution process may continue for plates 48 f, h,j, and l, until the fluid reaches plate 48 n, which has no outlet port84 such that fluid does not pass through this plate except via its fluidoutlet 52.

In this manner, a series of microlayers comprising alternating fluidsfrom extruders 14 a and 80 may be formed on microlayer stem 46. Forexample, if extruder 14 a supplied EVOH and extruder 80 supplied PA6,the resultant microlayered fluid mass 60 would have the structure:

-   -   EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH

The fluids from extruders 14 a and 80 may be the same or different suchthat the resultant microlayers in microlayered fluid mass 60 may havethe same or a different composition. Only one extruder may be employedto supply fluid to the entire microlayer assembly 34, in which case allof the resultant microlayers will have the same composition.Alternatively, three or more extruders may be used to supply fluid tothe microlayer assembly 34, e.g., with each supplying a different fluidsuch that three different microlayer compositions are formed inmicrolayered fluid mass 60, in any desired order, e.g., abcabc;abbcabbc; abacabac; etc.

Similarly, the fluid(s) directed through the distribution plate(s) 32may be substantially the same as the fluid(s) directed through themicrolayer assembly 34. Alternatively, the fluid(s) directed through thedistribution plate(s) 32 may be different from the fluid(s) directedthrough the microlayer assembly. The resultant tubular film may havethick layers and microlayers that have substantially the samecomposition. Alternatively, some of the thick layers from distributionplates 32 may be the same as some or all of the microlayers frommicrolayer plates 48, while other thick layers may be different fromsome or all of the microlayers.

In the illustrated example, the extruders and supply passages fordistribution plates 32 d-e are not shown. One or both of such plates maybe supplied from extruder 14 a, 14 b, and/or 80 by appropriatearrangement of vertical supply passages 72, 86, through-holes 74, and/oroutlet ports 84 of the upstream distribution plates 32 and/or microlayerplates 48. Alternatively, one or both distribution plates 32 d-e may notbe supplied at all, or may be supplied from a separate extruder, such asan extruder in fluid communication with primary manifold 76 and avertical supply passage 72 that extends through distribution plates 32a-c and microlayer assembly 34, e.g., via appropriate alignment of thethrough-holes 74 of plates 32 a-c and microlayer assembly 34 to create afluid transport passage through die 12, leading to fluid inlet 50 ofdistribution plate 32 d and/or 32 e.

If desired, one or more of the distribution plates 32 and/or microlayerplates 48 may be supplied with fluid directly from one or moreextruders, i.e., by directing fluid directly into the fluid inlet of theplate, e.g., from the side of the plate, without the fluid being firstrouted through one of manifolds 76 or 78 and/or without using a verticalsupply passage 72, 86. Such direct feed of one or more plates 32 and/or48 may be employed as an alternative or in addition to the use ofmanifolds and vertical supply passages as shown in FIG. 2.

The foregoing description of preferred embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention.

What is claimed is:
 1. A die for coextruding a plurality of fluidlayers, comprising: a. a primary forming stem; b. one or moredistribution plates, each of said plates having a fluid inlet and afluid outlet, the fluid outlet from each of said plates being in fluidcommunication with said primary forming stem and structured to deposit alayer of fluid onto said primary forming stem having a thickness D; andc. a microlayer assembly, comprising (1) a microlayer forming stem, and(2) a plurality of microlayer distribution plates, each of saidmicrolayer plates having a fluid inlet and a fluid outlet, the fluidoutlet from each of said microlayer plates being in fluid communicationwith said microlayer forming stem and structured to deposit a microlayerof fluid onto said microlayer forming stem having a thickness M, saidmicrolayer plates being arranged to provide a predetermined order inwhich the microlayers are deposited onto said microlayer forming stem toform a substantially unified, microlayered fluid mass on said microlayerforming stem, wherein, said thickness M of said microlayers is less thansaid thickness D of said fluid layer from said distribution plate, andsaid microlayer forming stem is in fluid communication with said primaryforming stem such that said microlayered fluid mass flows from saidmicrolayer forming stem and onto said primary forming stem in order tominimize interfacial flow instabilities.
 2. The die of claim 1, whereinsaid distribution plate has a thickness ranging from about 0.5 to about2 inches and said microlayer distribution plates have a thicknessranging from about 0.1 to about 0.5 inch.
 3. The die of claim 1, whereinsaid microlayer distribution plates have one or more flow channelsconnecting said fluid inlet with said fluid outlet, said flow channelshaving a spiral-shaped configuration.
 4. The die of claim 1, whereinsaid microlayer distribution plates each have an orifice extendingthrough said plate; said fluid outlet of each of said microlayerdistribution plates is positioned adjacent to said orifice; and saidmicrolayer forming stem extends through the orifice of each of saidmicrolayer distribution plates.
 5. The die of claim 1, wherein saidprimary forming stem and said microlayer forming stem are substantiallycoaxially aligned with one another.
 6. The die of claim 5, wherein saidmicrolayer forming stem is external to said primary forming stem.
 7. Thedie of claim 1, wherein said distribution plates and said microlayerassembly are axially positioned along said primary forming stem; and thefluids from said distribution plates and said microlayer assembly flowin an axial direction along said primary forming stem.
 8. The die ofclaim 7, wherein said distribution plates are located upstream of saidmicrolayer assembly.
 9. The die of claim 7, wherein said microlayerassembly is located upstream of said distribution plates.
 10. The die ofclaim 7, wherein said microlayer assembly is positioned between one ormore upstream distribution plates and one or more downstreamdistribution plates.
 11. The die of claim 1, wherein said microlayerassembly comprises at least about 5 microlayer plates.
 12. The die ofclaim 11, wherein said microlayer assembly comprises at least about 10microlayer plates.
 13. The die of claim 1, further including one or moreadditional microlayer assemblies.
 14. The die of claim 1, wherein theratio of M:D ranges from about 1:1 to about 1:8.
 15. The die of claim 1,wherein said microlayer thickness M ranges from about 1-20 mils; andsaid layer thickness D from said distribution plate ranges from about20-100 mils.
 16. The die of claim 1, wherein each of said microlayersthat are deposited onto said microlayer forming stem have physicalintegrity and independent physical properties; and said microlayeredfluid mass merges with said fluid layer from said distribution plate onsaid primary forming stem with a mass flow rate that more closelyapproximates that of said distribution plate layer, thereby increasingan ability of said microlayers in said fluid mass to retain saidphysical integrity and independent physical properties.
 17. The die ofclaim 1, wherein said microlayer forming stem is separate from saidprimary forming stem.
 18. The die of claim 1, wherein said thickness Mof said microlayers is substantially the same.
 19. The die of claim 1,wherein said thickness M of said microlayers is different among at leasttwo of said microlayers.